Operations at the airline were expected to be under more strain Monday than as there are far more flights packed in to normal scheduling.
BA has warned knock-on effects from this walkout will carry on throughout this week and workers are due to strike again from Saturday for four days if the dispute is not resolved.
At Heathrow's Terminal 5, German couple Carolin and Stefan Marquardt had a seven-hour wait for their flight home to Stuttgart, after being forced to cut their vacation in India short because their original flight from Bangalore was canceled.
"I've been stressed by it all," said Carolin Marquardt. "It's not a very nice end to our vacation, we haven't had any sleep."
"I understand both sides of the disagreement, but it's bad for people like us," she added.
The Unite union and BA have both claimed victory over the walkout that has caused the airline to cancel over half its 1,950 flights normally scheduled over the period.
BA reported that nearly 98 percent of staff reported for work at Gatwick and more than half showed up at Heathrow, allowing it to reinstate a number of canceled flights.
However, Unite said that only 300 of its 2,200 cabin crew scheduled to work over the weekend turned up, and accused the airline of counting inbound crew to inflate the numbers of staff on duty.
BA stressed that it was legally obliged, as a listed company, to release accurate figures.
The acrimonious dispute with its workers is expected to be financially crippling for BA - analysts forecast the three-day walkout could cost the airline more than the 63 million pounds ($95 million) that Chief Executive Willie Walsh is trying to save through the changes to workers' pay and conditions.
The walkout is also bad news for Prime Minister Gordon Brown's Labour Party, which relies heavily on funding from the country's labor unions, and a gift for the main opposition Conservative Party, which is leading opinion polls ahead of a general election due within weeks.
The Conservatives are seeking to evoke memories of the difficulties the Labour government had in the 1970s, culminating in the mass strikes that became known as Britain's "winter of discontent" and led to the election of Conservative leader Margaret Thatcher in 1979.
Business group London First, whose members include many of London's internationally-based businesses, warned on Monday that the capital's reputation as a center for global trade was being damaged by the strike.
"Despite the best efforts of BA management and many staff to continue to put the interests of passengers first, the strike is reminiscent of a best-forgotten era," said London First Chief Executive Jo Valentine.
There was little sign of appeasement from either side on Monday as Unite joint leader Tony Woodley told a rally of striking workers at a football ground near Heathrow to stand strong against BA's attempts to "blackmail and browbeat" them into accepting worse pay and conditions.
The airline on Friday offered a compromise on a proposed pay freeze this year, offering a 3 percent rise next year and the year after and then an inflation-linked increase in 2013/14 capped at 4 percent. The other changes include a switch to part-time work for 3,000 staff and a reduction in cabin crew sizes from 15 to 14 on long-haul flights from Heathrow.
Woodley said that BA was employing the "economics of the madhouse" by spending tens of millions on contingency plans for the walkout, including leasing planes and crew from rival airlines.
For more info:
British Airways Strike Alert